Systemic Lupus Erythematosus (SLE) is a disease in which genetically determined immune abnormalities are potentially triggered by hormonal factors and other environmental stimuli. In order to clarify the effects of exogenous sex hormones in SLE we must better understand the relationship between endogenous sex hormones and disease activity. The primary objective of this study will determine whether women with SLE have significantly different sex hormone profiles (estradiol/progesterone) during the menstrual cycle than non-SLE women.